In NSX UI (System → User Management → Local Users tab), clicking on the vertical ellipsis to delete Local User accounts (such as audit, guestuser1, or guestuser2) is greyed out.
VMware NSX 4.2
Starting with NSX 4.1, in addition to the admin user in the Enterprise environment, any user with the Enterprise Admin role can add new local users and remove audit and guest users. To administer NSX Manager, you must log in as admin. Some account management privileges are extended to the Enterprise Admin role.
NSX Managers